Between iPhone OS versions 2.2.1 and 3.0, there were several security issues that went unresolved for months. That includes the browser.

Even if Apple decide to provide security updates, who wants to download 250+ MB for what should be no more than 5 MB (yes, it's arbitrary) in fixes? Even Safari on Mac OS X, while large at ~31 MB for 4.0.5, is somewhat manageable. Mozilla Firefox's 1.6 MB for 3.6.2 would be ideal.

I use Opera Mini on my phone and it's quite capable, even if it's a bit odd at times. Version 5.0 is somewhat broken, but they'll have that fixed by 5.2. I would hope that Apple recognise the value of a secondary browser not tied to the same security risk and allow Opera Mini and Mozilla Fennec, if there could be one.